Though Godzilla isn't listed as a threat, Tokyo has the dubious distinction of being the world's most vulnerable city when it comes to natural disasters, according to a report released Wednesday by reinsurance firm Swiss Re.

"When we look at river flood, storm surge, tsunami, wind storm and earthquake combined, the Tokyo/Yokohama region is the most at-risk city in the world," says Megan Linkin, natural hazards expert with Swiss Re. "There is a potential affected population of 57.1 million people who could be impacted by one or more of these natural disasters."

The report ranked more than 600 global metropolitan centers that are inhabited by 1.7 billion of the world's population, which produce a combined GDP of $35 trillion, half the world's total economic output.

"For the first time in human history, more people live in cities than in rural areas," the report states. "The United Nations expects 6.3 billion people — or 68% of the world's population — to be living in urban areas by 2050."

The study shows that floods endanger more city residents than any other natural peril, followed by earthquakes and storms.

The only U.S. city to make the "top 10" list of most-vulnerable world cities is Los Angeles, primarily because of its risk of earthquakes. L.A. ranked ninth on the list, behind eight cities and metro areas in Asia.

"Swiss Re's research shows that Los Angeles is the most at-risk city in the world outside of Asia," says Linkin. "The Los Angeles metro area is highly exposed to earthquakes," she adds. "There has not been a major earthquake to strike an urban U.S. center since 1906, and this study is a timely reminder of just how exposed the population of California is to earthquakes.

"In 1994, the Northridge earthquake was centered 20 miles outside of Los Angeles yet the insurance industry still ended up paying out $21 billion in claims," says Linkin. If you consider that Northridge is not nearly as densely populated as downtown Los Angeles, you begin to get a sense of how catastrophic an event in Los Angeles would be.

"We hope that the research in this report is used by decisionmakers in urban areas across the world to gain a better understanding of their exposure to natural catastrophes and take the necessary steps to better protect their citizens from the impacts of these events," says Linkin.